This invention relates to the recovery of bituminous coal in conventional froth flotation equipment. More particularly, the invention is directed to a reagent for treating a solid material disposed in a liquid medium and having an oxygen-controlled surface condition.
Bituminous coal is a porous material in which environmental gases, such as air, may be entrapped. There are volatile surface products in the coal which unite with oxygen on the surface of a coal particle. There is inorganic material generally referred to in the industry as ash content and includes oxides, carbonates and silicates. All of these factors contribute to the basic problem of an oxygen-controlled surface condition being present on particulate bituminous coal. It is well known in the coal flotation industry, that coal having an oxygen-controlled surface condition will not be wetted by liquid hydrocarbons which are normally used in coal flotation. Consequently, large amounts of coal have not been recovered but have been carried into the refuse ponds and piles wherever there has been a coal production facility.
Froth flotation processes and equipment have been used for many years in the coal recovery industry. Much agitation, both mechanically and through the use of bubbling air, is used to effect the desired flotation. In other words, the environment within which the coal is being treated for flotation is also filled with oxygen. Thus, the environment within the froth flotation process contributes significantly to the maintaining of the oxygen-controlled surface condition on the bituminous coal fines.
The bituminous coal also includes pyritic sulfur and organic sulfur. The presence of a high sulfur content in the coal causes it to become a low grade material which may cause unwanted sulfur compounds being released into the atmosphere when the coal is burned. Further, the coal cannot be used with such high sulfur contents for applications such as Sea-coal which is a high grade metallurgical coal. The presence of the sulfur in the coal effects the formation of sulfuric acid when the coal is mixed with water. The longer the coal stands in the water, the more acid the water becomes. The acid water effluent is difficult to dispose of. It is a particular problem where such an effluent is being dumped into water tributaries and streams.
Over the years, large deposits of unrecovered coal, flowing from froth flotation processes, has been collected in huge refuse ponds. These ponds may be totally below ground or have been collected in containers above ground. Literally, millions of tons of coal having an oxygen-controlled surface condition lies in these ponds. Vast amounts of the unrecovered bituminous coal is also collected in large piles subjected to the open atmosphere. This is a very basic disadvantage and significant problem associated with the use of the froth flotation equipment which incorporates the use of known flotation reagents.
U.S. Pat. No. 1,667,277 discloses a typical prior art froth flotation process using various types of reagents. Such a prior art operation is maintained in the presence of high oxygen environmental conditions. Chemically, the reagents used in this prior art process as well as other known processes incorporate the use of combined oxygen. Mechanically, the bubbling of air aggravates the oxygen-controlled surface condition on the bituminous coal fines.
Much of the raw bituminous coal sources presently providing a supply to existing froth flotation facilities, contains large amounts of oxidized coal. As noted above, the froth flotation equipment and the existing reagents used in this equipment, are not capable of recovering this oxidized coal. Consequently, large amounts of coal are not recovered. Furthermore, because of the lack of sufficient coal from existing sources, froth flotation equipment is not being used to its fullest extent. The attendant disadvantages to this type of situation is deemed obvious.